This invention relates to relative navigation, precision rendezvous and station keeping, datalinks, and specifically to using a datalink for precision rendezvous and station keeping.
Future uninhabited combat air vehicles (UCAVs) and other aircraft will require precise relative navigation capability to perform many mission functions. In most situations differential GPS techniques suitably augmented with inertial data will probably suffice for aircraft relative navigation. However the need to preserve aircraft operations in the case of denial of GPS implies that a self-contained relative navigation capability needs to be available, particularly in tactical operations. A specific example is automated refueling of UCAVs.
With piloted aircraft aerial refueling, relative navigation for the rendezvous is accomplished with TACAN and barometric altimeters. Fine navigation during connect, fueling, and disconnect is done visually by the pilot and tanker boom operator. For the rendezvous phase, the major problem with TACAN is that it is not a low-observable waveform. For the UCAV, precise, low-latency three-dimensional relative navigation is required throughout the entire capture/connect/fueling/disconnect process with the tanker boom operator having control over the UCAV at close range.
In a UCAV automated aerial refueling (AAR) system, coarse position reporting during rendezvous is sufficient. High accuracy is not required with standalone GPS positioning being adequate. For communications with the UCAV a low-observable communications datalink with long range is needed with a modest data rate being required such as less than a 1-Hz update rate and less than 20-kbps data rate. Networking must be flexible in the datalink communications system.
High-accuracy relative positioning is required during capture and refueling of the UCAV. A system wherein a tanker sends code and carrier measurements to the UCAV to compute a real-time relative navigation solution is needed. A 10-Hz update rate for GPS data and a 20-Hz rate for inertial navigation system (INS) data are required for real time control. A 60-kbps data rate is required with high integrity/reliability for data communications. A networked communications system with multiple UCAVs with varying update rates is desired.
The DARPA Tactical Targeting Network Technology (TTNT) datalink offers low-latency, high-bandwidth, and low-observable characteristics that are particularly well-suited to UCAV applications. The TTNT datalink may be used for relative navigation and may be applied to UCAV aerial refueling and station keeping. A TTNT-based three-dimensional relative navigation system is needed that also provides a backup for relative GPS and an integrity monitor for relative GPS. A system concept based on TTNT that can provide the necessary relative accuracy independent of external navigation signals is needed.